<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <title>Document</title>
  <style type="text/css">
    *{margin:0;padding:0;list-style:none;}
    a{text-decoration: none;color: #fff;}
    #flash{width: 730px;height: 454px;margin: 100px auto;position: relative;cursor: pointer;}
    #pic li{position: absolute;top: 0;left: 0;z-index: 1;display: none;}
    #num{position: absolute;left: 40%;bottom: 10px;z-index: 2;cursor:default;}
    #num li{float: left;width: 20px;height: 20px;border-radius: 50%;background: #666;margin: 3px;line-height: 20px;text-align: center;color: #fff;cursor: pointer;}
    #num li.active{background: #f00;}
    .arrow{height: 60px;width: 30px;line-height: 60px;text-align: center;display: block;position: absolute;top:45%;z-index: 3;display: none;}
    .arrow:hover{background: rgba(0,0,0,0.7);}
    #flash:hover .arrow{display: block;}
    #left{left: 2%;}
    #right{right: 2%;}
  </style>
  <script type="text/javascript">
    function $(id) {
      return typeof id==='string'?document.getElementById(id):id;
    }
    window.onload=function(){
      var index=0;
      var timer=null;
      var pic=$("pic").getElementsByTagName("li");
      var num=$("num").getElementsByTagName("li");
      var flash=$("flash");
      var left=$("left");
      var right=$("right");
      //单击左箭头
      left.onclick=function(){
        index--;
        if (index<0) {index=num.length-1};
        changeOption(index);
      }
      //单击右箭头
      right.onclick=function(){
        index++;
        if (index>=num.length) {index=0};
        changeOption(index);
      }      
      //鼠标划在窗口上面，停止计时器
      flash.onmouseover=function(){
        clearInterval(timer);
      }
      //鼠标离开窗口，开启计时器
      flash.onmouseout=function(){
        timer=setInterval(run,2000)
      }
      //鼠标划在页签上面，停止计时器，手动切换
      for(var i=0;i<num.length;i++){
        num[i].id=i;
        num[i].onmouseover=function(){
          clearInterval(timer);
          changeOption(this.id);
        }
      }    
      //定义计时器
      timer=setInterval(run,2000)
      //封装函数run
      function run(){
        index++;
        if (index>=num.length) {index=0};
        changeOption(index);
      }
      //封装函数changeOption
      function changeOption(curindex){
        console.log(index)
        for(var j=0;j<num.length;j++){
          pic[j].style.display="none";
          num[j].className="";
        }
        pic[curindex].style.display="block";
        num[curindex].className="active";
        index=curindex;
      }
    }
  </script>
</head>
<body>
  <div id="flash">
    <ul id="pic">
      <li ><img src="http://img13.360buyimg.com/da/jfs/t2242/262/578407619/87636/4ffe0c5/56187ed2Nfed9a5b3.jpg" alt=""></li>
      <li style="display:block"><img src="http://img13.360buyimg.com/da/jfs/t2143/111/577347825/96150/e27180bd/561889b3N42ee62b5.jpg" alt=""></li>
      <li><img src="http://img20.360buyimg.com/da/jfs/t1825/234/1750370913/97529/b9229832/560b5ad3N054605f7.jpg" alt=""></li>
      <li><img src="http://img10.360buyimg.com/da/jfs/t2026/215/573306345/95654/a0211937/5618a735N1b3d8423.jpg" alt=""></li>
      <li><img src="http://img20.360buyimg.com/da/jfs/t2065/362/579832759/78899/6f349917/5618c680N3752bacc.jpg" alt=""></li>
      <li><img src="http://img10.360buyimg.com/da/jfs/t2023/45/384256123/101565/9b6e5daf/5604bdceN8c7d2ccf.jpg" alt=""></li>
    </ul>
    <ol id="num">
      <li class="active">1</li>
      <li>2</li>
      <li>3</li>
      <li>4</li>
      <li>5</li>
      <li>6</li>
    </ol>
    <a href="javascript:;" class="arrow" id="left"><</a>
    <a href="javascript:;" class="arrow" id="right">></a> 
  </div>
</body>
</html>